<customer 
    xmlns="http://www.example.com/foo" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    id="123">
    <firstName>Jane</firstName>
    <lastName xsi:nil="true"/>
    <phoneNumbers>
        <phoneNumber type="work">555-1111</phoneNumber>
    </phoneNumbers>
</customer>